This invention relates to a process and catalyst for the incineration of a combustible hydrocarbon feedstock. More particularly, this invention relates to a process and catalyst for the fluid bed incineration of a combustible feedstock in the presence of a combustion promoter catalyst where low levels of flue gas carbon monoxide can be attained at favorably lower combustion temperatures.
The development of efficient methods for reducing the volume of wastes, including hydrocarbon waste, is becoming an important industry objective. Refineries, petrochemical plants, and public utilities often must dispose of waste hydrocarbon or hydrocarbon fuel that cannot be costeffectively refined or modified into saleable product. Alternatively, land-filling unsalable hydrocarbon is costly, and the costs escalate with the volume of hydrocarbon, the hazard and toxicity of the hydrocarbon, and its ease of handling. Moreover, landfill space is becoming more and more limited. Fluid bed incinerators (FBI) have been widely used by industry and public utilities to reduce the volume, toxicity, and facilitate ease of handling of unsalable hydrocarbon by combusting a substantial portion of the hydrocarbon to carbon dioxide and water.
FBI generally comprise feedstock preparation facilities, a reactor section, flue gas handling facilities, and solids handling facilities. The reactor section is where the combustion reaction occurs and can comprise a reactor vessel having a bed of an inert heat transfer media. For purposes of this invention, the term "inert heat transfer media" is defined as a particulate media substantially incapable of catalytically converting high boiling hydrocarbon into lower boiling gasoline and distillate. The heat transfer media can be a silica sand or chemical pellets and can include ash produced in the combustion process. The heat transfer media functions as a heat reservoir for vaporizing water present in the feedstock. The energy supplied to the heat transfer media from the heat of combustion of the FBI feedstock provides most of the heat requirements for feedstock water vaporization but can be supplemented by auxiliary fuel usage.
A problem attendant to FBIs and other processes relying on combustion steps such as coal gasification and fluidized bed coking is the adverse effects of incomplete combustion to carbon monoxide. Incomplete combustion of unsalable hydrocarbon is environmentally deleterious and represents a wasted source of energy. The further oxidation of carbon monoxide to carbon dioxide releases approximately 4,350 Btu/lb of carbon monoxide oxidized.
Industrial and utility operators of FBIs have, in some cases, overcome incomplete combustion conditions by increasing excess oxygen levels in the flue gas zone or increasing the flue gas zone temperature, both facilitating higher conversion of carbon monoxide to carbon dioxide. Increasing excess oxygen levels is often very costly due the energy costs inherent with adding additional combustion air or oxygen volume to the flue gas zone, heating this excess volume from ambient conditions to combustion stack outlet temperatures, and discharging this volume to the atmosphere. Increasing the flue gas zone temperature adversely increases the level of metal compound emissions to the atmosphere due to increased vaporization of these materials in the reactor vessel. Moreover, increasing the flue gas zone temperature inefficiently increases radiant heat losses through the combustion device hardware and, more seriously, causes damage to device hardware.
High flue gas and combustion zone temperatures greatly reduce the hardware life of combustion devices such as FBIs. FBIs can operate at temperatures of from about 500.degree. F. to about 3000.degree. F. and often must resist abrasion caused by fluidized solids circulating at high velocities. FBIs, as well as most high temperature combustion devices, are generally equipped with specialized refractory, designed to resist high temperature and erosive environments. In spite of modern refractory technology, high temperature operation greatly increases the occurrences of refractory damage, damage to the FBI steel structures, and the frequency and duration of facility downtime.
While there exists a great need to recognize, identify, and solve the environmental and energy related problems associated with incomplete combustion in the process of fluid bed incineration, the art has been devoid of teachings, and industry has largely acquiesced to the costly solutions described above.
Carbon monoxide combustion promotion techniques, however, have been taught for use with other unrelated processes requiring a hydrocarbon combustion step. These techniques have met with varying degrees of success.
Carbon monoxide combustion promotion has been performed in fluid catalytic cracking facilities. U.S. Pat. Nos. 4,146,463 (Radford et al.), 4,204,945 (Flanders et al.), 4,252,632 (Mooi), and 4,435,282 (Bertolacini et al.) all disclose processes for enhanced conversion of carbon monoxide to carbon dioxide in the regenerator section of a fluid catalytic cracking unit using a combustion-promoting catalyst. These catalysts are either modified cracking catalysts or are added as a supplement to conventional cracking catalysts and are reacted with, attrited, and replenished along with the cracking catalyst before the combustion promoter catalyst can be deactivated or physically destroyed. As a result, particle attrition through regenerator cyclone systems, particle durability, particulate fluidization, and particulate mixing have not been as controlling and critical in nature as in the process of the present invention. Moreover, promoter catalyst deactivation is less critical since the promoted catalyst is continuously replaced. In practice, a fluid catalytic cracking combustion promoter would not achieve the process objectives of the fluid bed incineration catalyst and process of the present invention (see Example 24).
It is therefore an object of the present invention to provide a process and catalyst for fluid bed incineration that reduces air pollution by achieving reduced flue gas carbon monoxide levels emitted to the atmosphere.
It is another object of the present invention to provide a process and catalyst for fluid bed incineration that reduces air pollution by achieving reduced flue gas metals levels emitted to the atmosphere.
It is another object of the present invention to provide a process and catalyst for fluid bed incineration that achieves reduced levels of hydrocarbon and other products of incomplete combustion (PIC'S) at lower operating temperatures.
It is yet another object of the present invention to provide a process and catalyst for fluid bed incineration that extends incinerator equipment life, reduces maintenance costs, and reduces the frequency and duration of facility downtime.
It is yet another object of the present invention to provide a process and catalyst for fluid bed incineration with reduced energy costs.